On 30/06/11 00:34, Bruno Haible wrote:
> Hi Pádraig,
>
>> The following shows I think that iconv is bypassing stdio and buffering
>> internally?
>>
>> (echo; sleep 3; echo) | ltrace iconv -f ASCII
>
> Indeed, the glibc 'iconv' does not use stdio apparently:
>
> __libc_start_main(0x402a00, 3, 0x7fff76b92d68, 0x409c90, 0x409c80 <unfinished
> ...>
> setlocale(6, "")
> = "de_DE.UTF-8"
> textdomain("libc")
> = "libc"
> argp_parse(0x60d2e0, 3, 0x7fff76b92d68, 0, 0x7fff76b92c5c)
> = 0
> strchr("ASCII", '/')
> = NULL
> strchr("", '/')
> = NULL
> iconv_open(0x409daf, 0x7fff76b946e6, 0, 0x53494c4300494900,
> 0xfefefefefefefeff) = 0x613080
> fileno(0x7f4c6e9726a0)
> = 0
> realloc(NULL, 32768)
> = 0x00615100
> read(0, "\n", 32768)
> = 1
> read(0, "\n", 32767)
> = 1
> read(0, "", 32766)
> = 0
> iconv(0x613080, 0x7fff76b8ab38, 0x7fff76b8ab30, 0x7fff76b92b48,
> 0x7fff76b92b40) = 0
> ...
>
>> The stdbuf man page notes that:
>>
>> NOTE: If COMMAND adjusts the buffering of its standard streams (`tee'
>> does for e.g.) then that will override corresponding settings changed
>> by `stdbuf'. Also some filters (like `dd' and `cat' etc.) don't use
>> streams for I/O, and are thus unaffected by `stdbuf' settings.
>
> This paragraph is written in a way that does not make the implications
> very clear. How about the attached patch, meant to show the restrictions more
> prominently?
>
>
> 2011-06-29 Bruno Haible <[email protected]>
>
> * doc/coreutils.texi (stdbuf invocation): Mention the restrictions on
> the command more prominently.
>
> --- doc/coreutils.texi.orig Thu Jun 30 01:31:13 2011
> +++ doc/coreutils.texi Thu Jun 30 01:30:54 2011
> @@ -15398,6 +15398,17 @@
> stdbuf @var{option}@dots{} @var{command}
> @end example
>
> +@var{command} must start with the name of a program that
> +@enumerate
> +@item
> +uses the ISO C @code{FILE} streams for input/output (note the
> +programs @command{dd} and @command{cat} don't do that),
> +
> +@item
> +does not adjust the buffering of its standard streams (note the
> +program @command{tee} is not in this category).
> +@end enumerate
I'll apply this.
I'll might also add a note about fread() blocking (which POSIX requires)
and that setting no _buffering_ doesn't impact that.
cheers,
Pádraig.
